c# - DropDownList is not storing values -

i working on e-commerce app , problem in showing quantity of items purchased. dropdownlist shows option change quantity, in gridview , has selectedindexchanged event. event code works fine when there two(or more) products , change quantity of 1 row , change other rows's quantity, previous row quantity set default "1" while total price column shows multiplication of price , quanity set dropdownlist.

my dropdownlist code:

<asp:templatefield headertext="qty">                     <edititemtemplate>                         <asp:textbox id="textbox1" runat="server"></asp:textbox>                     </edititemtemplate>                     <itemtemplate>                         <asp:dropdownlist id="ddlqty" runat="server" autopostback="true"                              onselectedindexchanged="ddlqty_selectedindexchanged">                             <asp:listitem>1</asp:listitem>                             <asp:listitem>2</asp:listitem>                             <asp:listitem>3</asp:listitem>                             <asp:listitem>4</asp:listitem>                             <asp:listitem>5</asp:listitem>                         </asp:dropdownlist>                     </itemtemplate>                 </asp:templatefield> 

my c# code selectedindexchanged , gridview rowdataboundevent:

protected void ddlqty_selectedindexchanged(object sender, eventargs e)     {         dropdownlist ddlqty =(dropdownlist)sender;         int rowindex = int.parse(ddlqty.attributes["rowindex"].tostring());         viewstate["index"] = rowindex;         viewstate["i"] = ddlqty.selectedvalue;          decimal price = convert.todecimal(ds.tables[0].rows[rowindex]["price"].tostring());         decimal totalprice = price * convert.toint32(ddlqty.selectedvalue);         ds.tables[0].rows[rowindex]["totalprice"] = totalprice;         gridview1.datasource = ds;         gridview1.databind();         ds.tables[1].rows[0]["totalprice"] = decimal.parse(ds.tables[1].rows[0]["totalprice"].tostring()) + totalprice - convert.todecimal(ds.tables[0].rows[rowindex]["price"].tostring());         gridview1.footerrow.cells[2].text = "total amount =";         gridview1.footerrow.cells[3].text = ds.tables[1].rows[0]["totalprice"].tostring();     }     protected void gridview1_rowdatabound(object sender, gridviewroweventargs e)     {         if (e.row.rowtype == datacontrolrowtype.datarow)         {             dropdownlist ddl = (dropdownlist)e.row.findcontrol("ddlqty");             ddl.attributes.add("rowindex", e.row.rowindex.tostring());             if (viewstate["index"] != null)             {                 if (e.row.rowindex.tostring() == viewstate["index"].tostring())                 {                     ddl.selectedvalue = viewstate["i"].tostring();                 }             }          }     } 

i attaching image make more clear.

i think grid binding on each postback made dropdownlist, changing 1 value overwrite formerly stored value in vs. should try storing these values list, appending changes instead of replacing each time.

imho, anyway, go setting autopostback properties false, , updating row calculations client-side, validating on server side on submit.